Vetter: Why no 2D Userspace API in DRM?

Posted Aug 23, 2018 11:26 UTC (Thu) by daniels (subscriber, #16193)
In reply to: Vetter: Why no 2D Userspace API in DRM? by excors
Parent article: Vetter: Why no 2D Userspace API in DRM?

Yes, Imagination helpfully conflated the two concepts into the 'tile-based deferred rendering' catchphrase. GPUs can be tiled or not, deferred or immediate. There's a huge mix of both around. The only reason I brought it up is because the original poster conflated the two, and to point out that tiled render targets are not the same thing as using quads rather than triangles as a primitive.

Vetter: Why no 2D Userspace API in DRM?

Posted Aug 23, 2018 12:43 UTC (Thu) by excors (subscriber, #95769) [Link]

As far as I can tell, what Imagination means by "deferred" in TBDR is that fragment shading is deferred until after visibility is completely determined, specifically using their patented hidden surface removal technique. That's what they claim makes them unique and the best.

Other mobile GPUs (which Imagination calls TBR, i.e. not deferred) are basically the same, they just use different (perhaps slightly less optimal) hidden surface removal techniques. They still defer rasterisation until after the entire frame has been submitted and vertex-processed and binned. So the TBR/TBDR distinction is not much more than a marketing tactic, and I think it's sensible to just use the term "tile-based" for all of those GPUs, because their whole pipeline is fundamentally designed around tiles.

That's very different from NVIDIA's Maxwell, which still processes draw calls sequentially, and just uses one extra level of tiles when rasterising compared to older GPUs (~256x512 split into 16x16 split into 4x8 split into 2x2). So I'm just quibbling about grouping that together with the other 'tile-based' GPUs because it's not the same at all, except in the trivial sense that every GPU uses some kinds of tiles somewhere.

Anyway, I don't mean to disagree with your point, I just think that NVIDIA video/article spread misinformation about Maxwell being much more similar to mobile GPUs than it really is, and I can't resist the urge to try to clarify that whenever it comes up :-)